As optical discs, compact discs (hereinafter referred to as “CDs”) are used in increasing numbers. Audio data is recorded in a CD, by generating blocks of audio data, generating error correction codes, performing EFM (Eight to Fourteen Modulation) on the data blocks, and effecting NRZI (Non Return to Zero Inverted) modulation on the EFM-modulated data blocks.
As the result of the EFM modulation, the audio data is recorded in the CD, in the form of pits and lands that are alternately repeated. The pits and the lands can have nine different lengths 3T to 11T, where T is the fundamental period of the channel clock signal. The pits formed in the CD have a length of 0.87 to 3.18 [μm], a width of about 0.5 [μm] and a depth of about 0.1 [μm]. The range of length, 0.87 to 3.18 [μm], corresponds to 3T to 11T.
The audio data recorded in the CD has been sampled at the frequency of 44.1 [kHz]. It is two-channel data that has been quantized in units of 16 bits. It is demanded that the audio data should represent high-quality sounds and should be multi-channel data. Additionally, the CD should be so designed that the existing CD players may reproduce data from them. Further, it is not desirable that only a short audio program can be recorded in one CD when the data presents high-quality sounds and is multi-channel data.
Moreover, it is now desired that different items of information or related items of information be reproduced from the same CD in various modes.